1. Field of the Invention
The present invention relates to a measuring apparatus and a support mechanism of a columnar work piece. Specifically, the present invention relates to a support for a measuring apparatus measuring an elongated, columnar work piece.
2. Description of Related Art
Measuring apparatuses measuring a shape of an elongated, columnar work piece are known (for example, http://www.komatsu-machinery.co.jp/HP/japanese/seihin_kousaku_gdb.html, Japanese Patent No. 3,569,622, Japanese Patent No. 4,331,486, and Japanese Patent No. 4,820,681). For example, in http://www.komatsu-machinery.co.jp/HP/japanese/seihin_kousaku_gdb.html, a measuring apparatus is disclosed which measures a shape of a columnar work piece such as a crank or cam shaft of an automobile. The measuring apparatus supports a top end portion of the columnar work piece so as to allow rotation of the columnar work piece and also supports a bottom end portion of the columnar work piece on a rotary table. In addition, while rotating the columnar work piece by rotating the rotary table, a stylus head makes contact from one side of the columnar work piece. This process is repeated in order, beginning at the top and moving toward the bottom.
When measuring the shape of the columnar work piece, the columnar work piece must be supported. Tapered centering holes are provided to both end surfaces of the columnar work piece, and a support mechanism supports the columnar work piece by fitting a conical or round body into these centering holes. The conical or round body used as such a clamp is referred to as a work piece centering device. The work piece centering device is monitored so as to have a prescribed shape, e.g. being highly conical or highly spherical (geometric deviation). The columnar work piece is centered by holding both end surfaces of the columnar work piece between such work piece centering devices and, moreover, accuracy of the centering holes (inwardly tapered surfaces) of the columnar work piece is calculated by inference from an inclination of the columnar work piece.
Although dimensions and tolerances are strictly managed for the work piece centering device, the devices nevertheless do not have completely regulated shapes (for example, a sphere). Calculating the centering hole (inwardly tapered surface) by inference from the work piece centering device is no more than an indirect measurement and cannot be said to accurately measure the shape of the columnar work piece itself. However, because the work piece centering device is fitted into the centering hole, it is also not possible to insert a probe into the centering hole. Accordingly, in conventional measuring apparatuses, it has not been possible to accurately measure a centering hole (inwardly tapered surface) of a columnar work piece.